Apparatus for remote position indication in a hydraulic positioning drive with a physically separated work cylinder

Abstract

A hydraulic positioning drive with a physically separated work cylinder which is connected via pressure oil lines, comprises a follow-up cylinder mounted at the positioning drive or in the immediate vicinity thereof, of the same type and the same volume as the work cylinder, which is hydraulically connected in series with the latter, so that its piston moves synchronously with that of the work cylinder. The piston position of the follow-up cylinder is sensed electrically and used as the positioner position. For synchronizing, both cylinders are connected in parallel from time to time and their pistons are run into the end positions.

What is claimed is: 
     
       1. In a hydraulic system which includes a hydraulic positioning drive having first and second hydraulic lines which alternately provide a pressure output and return line for forward and reverse positioning and work a cylinder containing a piston and having first and second connections for connecting to said hydraulic lines for driving said piston in opposite directions, the drive being located remotely from the work cylinder, apparatus for sensing the position of the work cylinder, disposed at a location in the vicinity of the drive, in order to provide a feedback signal for controlling the drive comprising: (a) a follow up cylinder, located in the vicinity of the positioning drive, of the same type and of the same volume as the work cylinder and similarly containing a piston and first and second connections for hydraulic lines, the first hydraulic line from said positioning drive coupled to the first connection of said follow up cylinder;   (b) a first three-way valve having its first inlet coupled to the second connection of said follow up cylinder;   (c) a second three-way valve having its second inlet coupled to the second connection of said first valve and its first inlet coupled to the first connection of said work cylinder, the second hydraulic line from said drive being coupled to the second connection of said work cylinder;   (d) a connection between the first hydraulic line of said positioning drive and the third inlet of said second valve; and   (e) a connection between the second hydraulic line of said positioning drive and the third inlet of said first valve, whereby by setting said first and second valves so that their first and second inlets are in communication, said work cylinder and follow up cylinder will be placed in series and by placing said valves so that their first and third inlets are in communication, said work cylinder and follow up cylinder will be connected in parallel.   
     
     
       2. Apparatus according to claim 1 and further including a bypass valve disposed across the two sides of said follow-up cylinder, the release pressure of which is lower than the operating pressure of the hydraulic system. 
     
     
       3. Apparatus according to claim 2 wherein the release pressure of said bypass valve is about 10% of the operating pressure.